1985 300SD too slow at take off - PeachParts Mercedes-Benz Forum

wallyj · #1 05-10-2009, 11:06 AM

Hello all, I have been faithfully searching but haven't found any answers so I thought I would post.

I have been driving my 617 powered SD for almost a year now and have done several fuel filter changes, and oil changes, lots of maintenance and keeping up on things. I have cleaned the boost line from the manifold, however the car is still so slow off the line it is almost scary to navigate a left turn at an intersection! That is too slow. It is fine on boost, and open highway.

Now I am not expecting a screamer here but after I have driven my parts car lately I noticed surprisingly it is much quicker off of the line, even before the boost really comes on (its an 82).

I have been thinking that perhaps there is something wrong with the injector pump, the car sat for an extensive amount of time before it came to me. probably 6 or 7 years as best I can tell. It did have a MB rebuilt motor in it previous to it sitting, so it has MAYBE 15000KM on a new motor.

I thought the lift pump might be flaky, however with the new motor, I hesitate to guess.

Does anyone know if the injectors or something in the pump may have gone bad from sitting that long without use?

The only other symptom is it occasionally stalls after a cold start and 2-4 seconds running. Then when you start it again you have to put my foot into it to get past what feels like a dead spot.

Could there be a small air leak somewhere? I have bleed the injectors at the lines, and the filter as well. Should there be any visible air in the clear fuel filter? I have some small bubbles that never seem to go away, some had suggested some are normal (my VW diesel is like that as well)

Any help would be appreciated.

pop & blow · #2 05-10-2009, 11:14 AM

so how slow is slow does it seem like it is going to die out or maybe acts like trans is slipping, you say it runs out ok at highway speeds, your problem could be the torque converter.

Diesel911 · #3 05-10-2009, 11:26 AM

I a curious to know why it sat for 6 years (maybe the Prior owner said something). Taking the time and expense to rebuild an Engine and letting the car sit for 6 years does not make sense to me.
Also, the Engine having been rebuilt does not mean that some other grief like overheating or running low on oil due to a Oil Cooler Hose leak could not have happend.

When I first got my Car it was also slow. The reason was that the Throttle Linkage was out of adjustment; extremely slopppy and not allowing the Throttle Arm on the IP to move all the way.
You said you did Maint. but you did not mention that the Valves have been adjusted or not; and how about that IP timing.
While the Valve Cover is off it would not hurt to line up the Camshaft Gear Timing mark with the Camshaft Tower timing mark and take a look at the Degree Marks the pointer Points to down on the Crankshaft Damper; it should be close to Zero (indicating Top Dead Center).
What is your Idle Speed?

Try swapping the Lift/Fuel Supply Pump from the parts Car to the Slow Car.

Whiskeydan · #4 05-10-2009, 11:36 AM

The '82 will be a bit quicker than the '85 due to the 3.07 vs 2.88 differential ratio.

Have you checked your timing chain enlongation?

Also, check the two o-rings on the bolt holding the secondary fuel filter. I've recently experienced air entering the fuel system there.

tangofox007 · #5 05-10-2009, 12:06 PM

Quote:

Originally Posted by wallyj

...the car is still so slow off the line it is almost scary to navigate a left turn at an intersection! That is too slow. It is fine on boost, and open highway.

I had the same problem. Adjusting the ALDA changed everything. I can squeal the tires from a dead stop now.

Whiskeydan · #6 05-10-2009, 12:28 PM

Quote:

Originally Posted by tangofox007

I had the same problem. Adjusting the ALDA changed everything. I can squeal the tires from a dead stop now.

"Tires" or tire?

blackestate · #7 05-10-2009, 02:16 PM

First thought to me, is the Trans shifting to 1st when stopped, or is the car trying to start in 2nd gear? That has been an issue if you search

cmbdiesel · #8 05-10-2009, 10:09 PM

I would recommend checking the throttle linkages as well. Mine were very sloppy when I first got my SD. The rod into the IP did not travel as far as it should. Short amount of time adjusting and testing on the highway, I had achieved greatly increased fuel delivery, resulting in much better acceleration. After that, then check your boost pressure, before and after the overboost protection solenoid, make sure your overboost system is functioning correctly. Only then would I consider going after the ALDA.

What are your 0-60 times?

cmbdiesel · #9 05-10-2009, 10:11 PM

You can check travel on the linkage that enters the IP by watching how far it travels when pedal is fully depressed, then removing it from the rest of the linkage assembly and manually moving it in and out.

tangofox007 · #10 05-10-2009, 11:41 PM

Quote:

Originally Posted by blackestate

First thought to me, is the Trans shifting to 1st when stopped, or is the car trying to start in 2nd gear?

Starting in 2nd is normal. Failing to downshift to 1st under load isn't; that could be a factor.

Lycoming-8 · #11 05-11-2009, 12:04 AM

Does the transmission on a W126 SD work differently from a W123 300D? Our car always starts off in 1st gear, although it may have been idling in 2nd at a stoplight to reduce the loping. Our 300D is an 83, so I guess there is a possibility of a change on the 85's ?!?

Gene Horr · #12 05-11-2009, 09:18 AM

Starting in second is not normal for the diesels though there may have been a particular version/model or two that I am unaware of. It was normal for some of the gasoline models during this period. The subject comes up occassionally with posters insisting that it starts in second, then they actually count the gear shifts, then either come back and admit their mistake or just disappear.

vstech · #13 05-11-2009, 09:49 AM

the NON turbo's do start in 2nd. most of the turbo's with the taller gears start in 1st. it's possible your turbo is not sending pressure to the alda. check the banjo bolt on the intake, and the valve on your firewall for blockage...

LUVMBDiesels · #14 05-11-2009, 10:11 AM

Here is what I did on my 1981 300SD to make it quicker off the line.

1) Valve adjustment --the valves will tighten up over time decreasing the amount of time they are open and the amount of flow they let in while open

2) Timing chain -- Make sure the chain is not stretched out

3) EGR -- I blocked off the EGR valve on the intake with a quarter.

4) IP linkages -- Here was a big change. My linkage would not open the IP all the way. I had about 1/8 inch left from where the linkage would stop moving to the hard stop in the IP. I adjusted the linkage to get the travel, then adjusted the idle speed stop and the linkage to the stop lever to get the idle at about 700RPM and the stop lever to work. All the adjustments had made the stop lever linkage too short to shut off the car!
This made a huge difference

5) Cleaned the banjo bolts, lines and switchover valve with carb cleaner.

6) ALDA -- adjusted it 1/2 turn CCW in 1/4 turn increments.

7) Added some slack to the bowden cable as the transmission was shifting at about 2000 RPM. I let it wind up to 3500 before shifting.

8) New style primer pump as mine was leaking and letting air into the fuel.

Give these a try it should not take more than an afternoon of tweaking to get the car moving off the line.